When the cross-country skier travels forward in a direct path, the skier rests for support alternately on each of his skis and exerts a thrusting movement forward while supporting himself on one of the skis, so as to cause the other ski to slide forward. During the performance of this alternating step, it is necessary to prevent the ski on which the skier supports himself from sliding backward, in order to ensure that the forward motion achieves maximum intensity.
Various devices preventing backward slippage of cross-country skis, while permitting its forward sliding motion with the minimum possible friction, are already known. For this purpose, a ski wax may be used to coat the sole of the ski and to ensure that this sole bites into the snow when a backward thrust is exerted on the ski, while reducing to a minimum the friction caused by the forward sliding of the ski. The ski wax is generally the most widely used backward slippage-inhibiting agent, but the delicacy required for its application and the inconvenience of its use are disadvantages. Indeed, waxing, which must occur before each skiing session, takes some time and is a delicate operation, since the wax must be changed when the quality of the snow varies. For this reason, other devices preventing backward slippage and incorporating mechanical anchoring mechanisms have been designed. So-called "scale"-type cross-country skis are today well known, in which the soles are shaped so as to embody, at least in the area of the ski runner, i.e., where the pressure of the skier's foot is exerted, a series of scales which, like "fish scales," are distributed over at least one part of the width and length of the ski, and which project slightly from the plane of the sole. The scales are arranged in inclined planes from top to bottom and from front to back so as to constitute, at their rear extremities, biting surfaces substantially perpendicular to the sole of the ski. Skis embodying scales thus provide for the effective anchoring of the ski in the snow during the forward thrusting motion, but they have one major disadvantage: the scales projecting beneath the sole increase considerably the friction of that sole on the snow during the forward sliding motion.
To remedy this problem, inventors have also considered equipping a cross-country ski with anchoring devices or movable "scales" mounted in a recess formed in the ski and opening into the sole of the latter. All of these "scales" are articulated around individual transverse axes and are attached to each other, while being distributed longitudinally, at a distance from one another. These movable scales may occupy a first anchoring position in the snow, in which all of the scales project downward under the sole of the ski and a second retracted position in which all of the scales are withdrawn into their recesses. In this device, because the scales are set at a distance from each other, there are gaps between them in which snow may become embedded. This snow may then hinder the operation of the backward slippage-prevention device by preventing the scales from pivoting freely. Furthermore, such a device has a relatively complex, burdensome structure because each scale can pivot around an individual transverse axis.